The invention relates to conveyors and, more particularly, to apparatus for driving a conveyor belt by means of rotating drive members such as sprockets.
In a wide variety of industries, it is common to transport goods within a factory on a modular conveyor belt formed of a plurality of interfitting plastic modules. Modular belts of any desired length or width can be fashioned by using a suitable number of modules. The modules include recesses sized to engage the teeth of sprockets mounted on shafts at one or more locations along the belt path. The belt is driven along its path by rotation of the sprockets.
Typically, a plurality of sprockets are mounted on a shaft in parallel, with each sprocket engaging the conveyor belt at a different location along the width of the belt. At least one of the sprockets is secured to the shaft to prevent lateral movement of the sprocket. The other sprockets are free to slide, or float, laterally along the shaft. The one or more fixed sprockets provide for proper alignment of the conveyor belt, while the floating sprockets can move along the shaft as the width of the conveyor belt varies with temperature and age. Allowing some of the sprockets to float eliminates stresses that would be produced in the belt if all the sprockets were fixed in place and also prevents the teeth of the sprockets from slipping out of mating engagement with the recesses of the belt.
Various arrangements are used in conventional conveyors to attach sprockets to a shaft. In some cases, sprockets are retained in position by C-rings snapped into individual circumferential grooves on each side of a sprocket. The precut grooves limit the positioning of sprockets to set axial positions along the shaft. Sprockets with circular bores for use on circular shafts are often used to drive conveyor belts. Frequently, the round shafts have an axial groove cut along the shaft to form a keyway to register a mating key extending from the sprocket into its circular bore. The engaged surfaces of the keyway and the key transmit the driving force from the shaft to the sprocket. Instead of having a keyway along the shaft, many conveyor systems have a raised key disposed axially along the outside of the shaft. A groove is formed along the bore wall of the sprocket to mate with the raised key in a driving engagement. In both of these arrangements, bolts or screws are often used to hold the sprockets in place. Screws through hub portions of a sprocket or through separate hub elements are tightened against the shaft to secure the sprocket in place. Because of the need to tighten the screw sufficiently to prevent the sprocket from coming loose, it is common, especially with plastic sprockets, for the threads of the screw hole through the sprocket to strip. Once the threads are stripped, the screw can fall out and contaminate the product, as well as free the sprocket from engagement with the shaft. Consequently, there is a need for a conveyor apparatus that has sprockets registered in driving engagement with a conveyor belt and able to float axially along the shaft or to be adjusted to any position along the shaft and secured there tightly.